A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the equatorial Pacific Ocean

Description

The seeding of an expanse of surface waters in the equatorial Pacific Ocean with low concentrations of dissolved iron triggered a massive phytoplankton bloom which consumed large quantities of carbon dioxide and nitrate that these microscopic plants cannot fully utilize under natural conditions. These and other observations provide unequivocal support for the hypothesis that phytoplankton growth in this oceanic region is limited by iron bioavailability., Cited By (since 1996):930, Oceanography

The behaviour of iron and other trace elements during the IronEx-I and PlumEx experiments in the Equatorial Pacific,

Description

Dissolved (< 0.4 μm) and particulate (0.4-5 μm and > 5 μm, leachable and refractory) trace elements were measured during the IronEx I and PlumEx experiments in October and November 1993 near the Galapagos Islands. Iron was measured in the enriched patch and at control stations over a 9 day period following fertilization. The dissolved iron was initially depleted at a rate that gave an iron half-life of 28-40 h. The loss rate gradually decreased, and dissolved iron concentrations did not decrease below about 0.25 nmol kg-1 throughout the experiment. These results were most consistent with a kinetic model that was second order in iron concentration for the scavenging removal of each iron fraction. Other trace elements measured did not change significantly either in concentration or partitioning during the IronEx I experiment. Biological production tracked iron concentrations over time, which suggests that productivity within the fertilized patch was regulated by the availability of iron. The PlumEx study consisted primarily of two transects, a meridional course to the east of the Galapagos Islands and a zonal section to the west. Surface dissolved iron was very low at all stations except those near the Galapagos Islands. Sections of trace metal and other properties distinctly confirm the upwelling of the Equatorial Undercurrent as it intersects the islands. This upwelling has a great effect on the surface distributions of the trace metals on the west side of the islands. Productivity within the mixed layer of this region is highly correlated with iron and nitrate. West of the islands highest productivity is found at stations with the highest iron. North of the Equatorial front, in nitrate-depleted waters, elevated iron concentrations do not enhance productivity., Cited By (since 1996):58, Oceanography, CODEN: DSROE, ,

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide., Cited By (since 1996):316, Oceanography, CODEN: SCIEA, ,

Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean,

Description

The idea that iron might limit phytoplankton growth in large regions of the ocean has been tested by enriching an area of 64 km 2 in the open equatorial Pacific Ocean with iron. This resulted in a doubling of plant biomass, a threefold increase in chlorophyll and a fourfold increase in plant production. Similar increases were found in a chlorophyll-rich plume down-stream of the Galapagos Islands, which was naturaly enriched in iron. These findings indicate that iron limitation can control rates of phytoplankton productivity and biomass in the ocean., Cited By (since 1996):749, Oceanography, CODEN: NATUA, ,

Excess major nutrients occur in offshore areas ranging from the tropical equatorial Pacific to the polar Antarctic. In spite of the great ecological differences in these environments, they share a common trait: iron deficiency. All of these areas are far from Fe-rich terrestrial sources and atmospheric dust loads in these regions are amongst the lowest in the world. Experiments were performed in three nutrient-rich areas: The Gulf of Alaska, the Ross Sea, and the equatorial Pacific. In general, populations without added Fe doubled at rates 11-40% of the expected maxima at various temperatures. The addition of nanomole quantities of Fe increased these doubling rates by factors of 2-3. In spite of the lack of Fe, tightly coupled phytoplankton/zooplankton communities seem to inhabit these major nutrient-rich areas. -from Authors, Cited By (since 1996):341, Oceanography, , , Downloaded from: aslo.org/lo/toc/vol_36/issue_8/1793.pdf (16 June 2014).

We designed a large-volume rosette sampler for collecting seawater with minimal trace metal contamination. The system uses eight modified 30-liter Go-Flo bottles secured to a Nylon II-coated stainless steel frame. The instrument is deployed with a dedicated winch with polyurethane-coated, three-conductor Kevlar hydroline. A prototype was used as part of the U.S. JGOFS Equatorial Pacific sampling program during spring and fall 1992. A redesigned model was used during the 1993 IronEx experiments and is currently being deployed in the Arabian Sea. The results of trace metal analyses collected on these cruises indicate that samples recovered are comparable to current single Go-Flo casts., Cited By (since 1996):28, CODEN: LIOCA, , , Oceanography, Downloaded from: www.aslo.org/lo/toc/vol_41/issue_6/1367.pdf (23 June 2014).

Here we report measurements of iron and aluminum in surface and subsurface waters during late March and late May of 2001 on transects between central California and Hawaii. A large cloud of Asian dust was detected during April 2001, and there was a clear signal in surface water iron due to aerosol deposition on the May transect. Iron and aluminum concentrations increased synchronously by 0.5 and 2 nM along the southern portion of the transect, which includes the Hawaii Ocean Time series (HOT) station, from background values in March (0.1 to 0.2 nM Fe). These changes occured in a ratio that is close to the crustal abundance ratio of the metals, which indicates a soil aerosol source. A vertical profile of dissolved iron was also measured at the HOT station in late April and this profile also shows a large increase near the surface. Direct observations of aerosol iron concentration at Mauna Loa Observatory on Hawaii indicate that aerosol concentrations were significantly lower than climatological values during this period. Soil aerosol concentrations along the transect were estimated using the real-time Navy Aerosol Analysis and Prediction System (NAAPS). The NAAPS results show a large meridional gradient with maximum concentrations in the boundary layer north of 30°N. However, the deposition of iron and aluminum to surface waters was highest south of 25°N, near Hawaii. There were only weak signals in the ecosystem response to the aerosol deposition., Cited By (since 1996):64, Oceanography, , , Downloaded from: http://onlinelibrary.wiley.com/doi/10.1029/2002GB002004/pdf (16 June 2014).